Lignin, a major component of plants, is a biomass resource that is ubiquitously present as an aromatic high molecular compound in plant cell walls. However, since plant-derived aromatic components composed mainly of lignin are composed of components with various chemical structures and have complex macromolecular structures, no effective technology has been developed for their use. The known utilization technologies involve separation and production of vanillin as a material for perfumes, from low molecular aromatic decomposition products of alkaline decomposition or other chemical decomposition of aromatic components. Currently, however, no method is known for effective use of large amounts of low molecular aromatic substances, other than vanillin, that are produced by chemical decomposition. Consequently, lignin produced in mass by paper-making processes has been burned as a substitute for heavy oil, without being effectively utilized.
The present inventors have found that plant aromatic components such as lignin are converted to low molecular mixtures containing vanillin, syringaldehyde, vanillic acid, syringic acid, protocatechuic acid or the like by chemical decomposition methods such as hydrolysis, oxidative decomposition or solvent decomposition, or physicochemical decomposition methods with supercritical water or supercritical organic solvents, and that these five compounds are converted to the single intermediate substance 2-pyrone-4,6-dicarboxylic acid, which can serve as starting materials for functional plastics or chemical products.
The present inventors have also reported a method of producing 2-pyrone-4,6-dicarboxylic acid from vanillin, syringaldehyde, vanillic acid, syringic acid or protocatechuic acid using transformants carrying genes coding for 4 different enzymes (benzaldehyde dehydrogenase, demethylase, protocatechuate 4,5-dioxygenase and 4-carboxy-2-hydroxy-6-semialdehyde muconate dehydrogenase) that participate in a multistage process for fermentative production of 2-pyrone-4,6-dicarboxylic acid (see Japanese Unexamined Patent Publication No. 2005-278549, for example).
However, while numerous intermediates in addition to 2-pyrone-4,6-dicarboxylic acid are known to be obtained by fermentative production from vanillin, syringaldehyde, vanillic acid, syringic acid and protocatechuic acid, their fermentative production processes have not been reported.